Tutorial: Why is moist air less dense than dry air? (HD)

Okay, so why is moist air less dense than dry air? Would it more sense that drier is less dense since it is less concentrated than moist air?
In this tutorial, we will learn why moist air is less dense, because this baffles many forecasters.
In order to understand this, we need to know a little bit of basic chemistry, and need to know about diatomic elements. As most of us know, gases are extremely light and need to be in pairs to be more stable. There are seven diatomic elements and they are: H2, N2, O2, F2, Cl2, I2, Br2, which are: hydrogen, nitrogen, oxygen, fluorine, chlorine, iodine and bromine. The most common gases in our atmosphere are Nitrogen and oxygen. Now Oxygen has an approximate atomic mass of 16, and nitrogen has an approximate atomic mass of 14. Now because they are in diatomic (di=double) , the typical atomic mass for oxygen is 32, and is 28 for nitrogen.
Water Vapor H2O has an atomic mass of 18. That is because Hydrogen only has only an atomic mass of 1 since it is the lightest element, and remember, Oxygen has an atomic mass of 16. In a water molecule, there are two hydrogen atoms; one at each side of the large Oxygen atom. So by adding the two hydrogen atoms and the oxygen atom, we will have a total atomic mass of 18 (1+1+16). With an atomic mass unit of 18, H2O is much lighter than diatomic Oxygen (32) and Nitrogen (28). Therefore the more water vapor that is available, the more the density of the air will decrease. Due to the fact that moist air is lighter than dry air, it is more buoyant, and will rise if a dry air mass is pushing against it. A good example of why moist air is susceptible to vertical motion is when an inflated balloon is placed in a tank of water. The balloon will rise as it is being displaced by the denser liquid; it would still try to rise even if you push against it.
Dry Lines
Now let us what happens when dry and moist air are placed side by side.
A dry line is the perfect example of moist air being less dense than drier air. A dry line is a region of substantial moisture gradient, which means that the humidity changes significantly over a small distance. Mesoscale convective complexes, squall lines, and even supercells tend to be associated with dry lines. That is why veteran storm chasers always look for areas of strong moisture gradient to determine the instability. A dry line is somewhat quasi-baroclinic, since the dry air pushes against the lighter moister air, forcing it to rise. Even without the aid of cold fronts, they still have adequate instability to kindle thunderstorm formation.

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[hereitcometh]

great job explaining. I was wondering and maybe you could break this down contrails or chemtrails --unburned aerosols in the exhaust -how would they effect moisture in our air would they affect natural dry lines-

[TheFaithseeker]

Great explanation :)

[kokopelli314]

Thanks for explaining 

[PaladinswordSaurfang]

just a pronunciation tip, it's flourEEN, chlorEEN, bromEEN, iodEEN, (not "eye"n) and u forgot At2

[nilanjana96]

suxx

[ZaphedBeebleBrox]

let me guess you must be japanese.. just curious.

[picaticatara]

becus is full of moist and delicious

[zwelis]

@anitabonghit123

This was quite good thank you

[anitabonghit123]

thankyou was informative